Open heart surgery is associated with a progressive fall in red cell 2-3 DPG during the course of perfusion. There is an accompanying increase in the hemoglobin affinity for oxygen. This decrease can be prevented by the administration of a solution of inosine, phosphate and pyruvate. It is anticipated that the postoperative depression can be corrected also. Thus the open heart patient would appear to represent a model to evaluate the influence of an acute shift of the oxyhemoglobin curve upon myocardial metabolism and function.